Usage of absolute transaction fees for escrow and payout transactions

[f321x]

The current implementation uses absolute transaction fees as the implementation is less complex. This works for testing as the transactions have roughly the same size every time. If there are more inputs to the escrow locking tx this scheme could fail, so a way to dynamically adjust the transaction fees to the size of the transaction and the mempool congestion should be implemented.
Affected function:

Escrow locking tx:
pub async fn create_escrow_psbt(
		&self,
		db: &Arc<CoordinatorDB>,
		taker_psbt_request: &OfferPsbtRequest,
	) -> Result<EscrowPsbt>

Payout tx:
pub async fn assemble_keyspend_payout_psbt(
		&self,
		payout_information: &PayoutData,
	) -> anyhow::Result<String>